Lindsay Lohan is starring in Scary Movie 5, but it's being reported that the 26-year-old starlet has "[blown] off rehearsals, missed her flight to the set and even bizarrely claimed she had walking pneumonia," according to the NY Post.

Lohan, who is set to have a cameo opposite Charlie Sheen, reportedly got cold feet after seeing that the script was mocking her. “It went pretty hard at Lindsay,” said a source, adding the script features a kiss with Sheen, and “she’d been freaking out about it for weeks.”

“Lindsay missed every meeting she had for the film, including script reads and wardrobe meetings,” the insider tells the Post. “Then she missed her flight to Atlanta on Sunday to shoot the movie. The producers had been getting signs Friday that she was a mess, and would not be fit to work.”

Yet another source tells the paper that Lohan tried to get out of doing the film claiming that she had walking pneumonia, and she even went to a hospital on Sunday to get her lungs checked. “She is under contract — so to get out of it, she had to prove that she was sick,” added a source. “She tried to prove she has walking pneumonia.”

The Post reports that Lohan did eventually make her way to the set, but only after she was threatened with a lawsuit and a private jet was sent to pick her up.

So what does Lindsay have to say about all this? A rep for the actress said, “These stories are untrue, and she is willingly fulfilling all of her obligations.”